Muhan's reign marked the pinnacle of Sogdian cultural influence in the Göktürk Empire. Sogdian culture was transmitted by merchants from Turpan who worked as ambassadors and advisers. The Sogdian language and script were used to govern the empire. The importance of Sogdians cannot be understated in keeping the early Turks safely outside of the Chinese cultural sphere. The Sogdian language and script were used to administer the empire, because it was the only written language in the cities under his control. After his death the title of qaghan passed to his younger brother Tapo. He was said to have red hair and blue eyes.[citation needed]

The second son of Tumen and third qaghan. He expanded the Göktürk Khanate and secured the borders against the last of the Rouran people. He conquered the Töle tribes in the west the Kitans in the east and the Kyrgyz in the north. Thus he expanded his state to all the former Xiong-Nu territory. His uncle Istämi autonomously ruled the far-west region (Kazakh Steppe) in his name. This was the beginning of the east/west division of power. He created an alliance with the Zhou kingdom, by marrying off his daughter, to oppose the Qi kingdom that was sheltering the Rouran.